Product category:
Industrial Drives/Controls
News Release from: Siemens Automation and Drives | Subject: Sikostart 3RW22
Edited by the Engineeringtalk Editorial
Team on 20 June 2003
Soft starter replaces variable speed
drive
The latest in soft starts is being used as an alternative to variable speed drives in a water supply pumping application.
The latest in soft starts is being used as an alternative to variable speed drives in a water supply pumping application Siemens soft starters are delivering surge pressure control - essential for both normal operation and during power supply fluctuations, at Bewdley Bank, a remote reservoir site three miles north of Hereford
High lift pumps deliver water from the River Wye to Bewdley Bank, which holds over 260,000m3 of water.
The water is then pumped to local customers and to a second reservoir at Dinmore seven miles away.
The higher-level storage at Dinmore is fed at a constant rate of 100litre/s by twin 355kW pumps that operate on a duty/standby basis.
As the reservoir at Dinmore has a far greater altitude than at Bewdley its system dynamics are extremely sensitive.
Variable speed drives were previously used to control the reservoir level and the amplitude of the surge wave pressures.
The situation at Bewdley Bank is particularly complex due to an inconsistent power supply.
Voltage dips and momentary losses of power, or brownouts, occur and voltage fluctuations are commonplace.
Despite the use of variable speed drives, the combination of hydraulic and electrical operating characteristics did not control the reservoir effectively and also gave fluctuating surge pressures.
Water hammer was also generating noticeable noise and vibration within the pumping station.
The impact on long term reliability and the potential of mechanical damage to pumps, valves and pipework, caused the site operators, United Utilities, considerable concern and a number of alternative solutions were examined.
The pump motors were in good condition but the variable speed drives had reached the end of their useful life, consequently the utility company was able to consider a wide range of options.
The prime design requirements were to have controlled starting and stopping (to limit the current draw), to attenuate pressure surges and to negate the impact of supply fluctuations.
The replacement of the variable speed drives was an obvious option whilst the use of soft starters offered massive savings if the design requirements could be achieved.
Conventional soft starters, that provide both a soft start and soft stop, are often suitable for the control of modest surge problems but the control of torque reduction during the stopping of the large motors at Bewdley Bank was an exceptional application outside of scope of these devices.
Fortunately, the latest soft start technology from Siemens was able to provide a successful low cost solution.
The Siemens Sikostart 3RW22 is an electronic, microprocessor controlled, motor control unit developed for these applications.
Suitable for the controlled startup, run-down, braking and energy saving operation of asynchronous three-phase motors, the unit is able to provide an integrated management system for motors up to 710kW.
As Mark Taylor, the United Utilities Unit Manager responsible for the Bewdley Bank upgrade commented recently: "The pumps with Sikostart 3RW22 control units were commissioned in January 2002 and have operated since then without problems.
The selection of the ramp-up time, pump-stop time and startup current limit has reduced surge wave pressures to a very low level.
The performance of the Siemens equipment has been very good and the latest technology has delivered the most cost effective solution by a substantial margin".
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